The present invention uses a mechanical analog to digital converter to measure distance. The distance measured is supplied in binary encoded decimal to an electronic decoder for decoding and subsequent decimal display.
The use of mechanical analog to digital converters is not new. However, the accuracy with which the analog information could be converted has been limited by physical requirements of the mechanical device. For example, it was not practical to detect changes in length on the order of a thousandth of an inch (0.001 inch) and convert it into a digital code representing the changes by using a simple mechanical device exclusively. The present invention offers a mechanical device which can be used to make measurements with an accuracy of this order of magnitude or better. A digital scale of binary is used which exhibits a one to one correspondence with discrete locations on the scale, and coded information at those locations. Photographic reducing techniques such as those used to make microfiche make it possible to encode information onto a scale at extremely small increments using extremely small characters so that output inaccuracies caused by the physical requirement that the characters occupy some finite area on the scale is very small. The net effect is that the range of distances input to the device which can result in unchanged digital output is extremely small.
The magnitude of the distance being measured is input to the device in terms of the location on the scale seen by a photoelectric detector. The information at that location is sensed and is subsequently used to control a digital display. The photoelectric detector is comprised of a magnifying lens, light conducting fibers, and phototransistors. Integrated circuits have been used to design a device which gives a digital readout of distance measurements and which has a size close to that of its conventional mechanical counterpart from which distance is interpreted by manually reading a linear scale.
An object of the present invention is to provide a practical device for making measurements of distance by means of mechanical input and to have the input information conveniently converted into a digital code for ease of transmission, electrical conversion, and display.